The present invention has to do with a device for automatically sharpening cartridge born slitter blades.
In a plant for manufacturing paper or other films or webs (for ease of description, the term "paper" will be used for all web materials), the paper is typically produced in large widths which are chosen for ease of handling in bulk. To produce paper in a desired set of smaller widths, a paper roll is unwound through a slitting machine, which slits the paper into the desired set of widths.
Referring to FIG. 1, a typical present day web slitting machine includes a number of web slitting assemblies, such as assembly 10, mounted on a transverse bar 14. Assembly 10 includes an upper carriage portion 16 and a blade cartridge 18, which includes a freely rotating disk-shaped slitter blade 20. The edge of blade 20 overlaps with a lower sharp-edged disk 22 so that together blade 20 and lower sharp-edged disk 22 present a scissors like action to a continuous web of material which is pulled through blade 20 and disk 22 by a drum or take-up reel (not shown). Blade cartridge 18 includes a dovetail channel 24 that engages with a dovetail bar 26 of upper carriage portion 16.
The advent of blade cartridges, such as cartridge 18, has greatly facilitated the sharpening of dull slitter blades. Prior to the introduction of blade cartridges, a slitter blade would be removed from its web slitting machine in a cumbersome operation, sharpened and replaced in a further cumbersome operation. With blade cartridges it is easy to snap a cartridge having a dull blade (a "dull cartridge") out of a machine, and quickly replace it with a cartridge having a sharp blade (a "sharp cartridge"). This approach minimizes machine down time and the labor of changing slitter blades. Dull cartridges are replaced by sharp cartridges from an inventory that is typically kept on hand near the web slitting machine. The dull cartridges are accumulated and taken to a shop where each blade is removed from its cartridge, sharpened by a skilled craftsman and reinstalled into a cartridge.
Although this system is a great improvement over previous systems, there are still significant problems. First, because an inventory of sharp cartridges must be kept on hand, the total number of cartridges that must be acquired is greater than would be necessary if the blades were sharpened more quickly and without the need for transport to a shop. Second, it is fairly expensive to sharpen blades manually, taking about 20 minutes of a skilled craftsman's time.
Although an automatic blade sharpener is highly desirable, a number of technical challenges must be met in order to create a practical device of this nature. First, an automatic blade sharpener ideally should easily accept and retain blades for sharpening. Second, the debris that is generated by the sharpening process must be prevented from disturbing the process. Third, there must be some way of controlling the process so that it produces a sharp blade without removing a great deal more blade material than is necessary. Finally, there must be some method of compensating for the increasing thickness of most slitter blades toward the blade center.